Multi-layer tubing having electrostatic dissipation for handling hydrocarbon fluids

ABSTRACT

An elongated multi-layer tubing having a first layer disposed radially innermost and having an inner surface capable of prolonged exposure to a fluid containing hydrocarbons and an outer surface spaced a first predetermined radial thickness from the inner surface, the first layer containing an extrudable, melt-processible thermoplastic. The tubing also includes a second layer connected to or bonded to the first layer and consists essentially of an extrudable, melt-processible thermoplastic capable of laminar adhesion with the first layer. At least one of the first and second layers can be resistant to permeation by hydrocarbons. The tubing includes a third layer connected to or bonded to the second layer and containing an extrudable, melt-processible thermoplastic.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 09/995,213, filed onNov. 26, 2001, which is a divisional of U.S. Ser. No. 09/405,757, filedSep. 27, 1999, which is a continuation of U.S. Ser. No. 08/639,421 filedApr. 29, 1996 (now U.S. Pat. No. 5,996,642), which is a continuation ofU.S. Ser. No. 08/234,298 filed Apr. 28, 1994 (now U.S. Pat. No.5,524,673), which is a continuation-in-part of co-pending U.S. Ser. No.07/896,824 (now U.S. Pat. No. 5,383,087); U.S. Ser. No. 07/897,304; U.S.Ser. No. 07/897,302; and U.S. Ser. No. 07/897,376, all filed on Jul. 11,1992; a continuation-in-part of co-pending U.S. Ser. No. 07/868,754filed on Apr. 14, 1992 and a continuation-in-part of co-pending U.S.Ser. No. 07/962,249, filed on Oct. 16, 1992.

FIELD OF THE INVENTION

The present invention relates to tubing for use in a motor vehicle. Moreparticularly, the present invention relates to a multi-layer tube whichcan be employed for transporting hydrocarbon fluids such as a fuel lineor vapor recovery line of a motor vehicle.

BACKGROUND OF THE INVENTION

[Single layer fuel lines and vapor return lines of synthetic materialssuch as polyamides have been proposed and employed in the past. Fuellines employing such materials generally have lengths of at leastseveral meters. It is important that the line, once installed, notmaterially change during the length of operation, either by shrinkage orelongation or as a result of the stresses to which the line may besubject during use.

It is also becoming increasingly important that the lines employed beessentially impervious to hydrocarbon emissions due to permeationthrough the tubing. It is anticipated that future Federal and stateregulations will fix the limit for permissible hydrocarbon emissions dueto permeation through such lines. Regulations which will be enacted instates such as California will fix the total passive hydrocarbonemission for a vehicle at 2 g/m² per 24 hour period as calculated byevaporative emission testing methods such as those outlined in Title 13of the California Code of Regulations, section 1976, proposed amendmentof Sep. 26, 1991. To achieve the desired total vehicle emission levels,a hydrocarbon permeation level for the lines equal to or below 0.5 g/m²per 24 hour period would be required. Finally, it is also imperativethat the fuel line employed be impervious to interaction with corrosivematerials present in the fuel such as oxidative agents and surfactantsas well as additives such as ethanol and methanol.

Various types of tubing have been proposed to address these concerns. Ingeneral, the most successful of these have been co-extruded multi-layertubing which employ a relatively thick outer layer composed of amaterial resistant to the exterior environment. The innermost layer isthinner and is composed of a material which is chosen for its ability toblock diffusion of materials, such as aliphatic hydrocarbons, alcoholsand other materials present in fuel blends, to the outer layer. Thematerials of choice for the inner layer are polyamides such as Nylon 6,Nylon 6.6, Nylon 11 and Nylon 12.

Alcohol and aromatics in the fluid conveyed through the tube diffuse atdifferent rates through the tubing wall from the aliphatic components.The resulting change in the composition of the liquid in the tubing canchange the solubility thresholds of the material so as, for example, tobe able to crystallize monomers and oligomers of materials, such asNylon 11 and Nylon 12, into the liquid. The presence of copper ions,which can be picked up from the fuel pump, accelerates thiscrystallization. The crystallized precipitate can block filters and fuelinjectors and collect to limit travel of the fuel-pump or carburetorfloat as well as build up on critical control surfaces of the fuel pump.

In U.S. Pat. No. 5,076,329 to Brunnhofer, a five-layer fuel line isproposed which is composed of a thick outer layer formed of Nylon 111 orNylon 12, a thick intermediate layer of Nylon 6, and a thin intermediatebonding layer between and bonded to the intermediate and outer layersformed of a polyethylene or a polypropylene. On the interior of the tubeis an inner layer of Nylon 6 with a thin intermediate solvent-blockinglayer formed of an ethylene-vinyl alcohol copolymer transposed between.The use of Nylon 6 in the inner fluid contacting surface is designed toeliminate at least a portion of the monomer and oligomer dissolutionwhich occurs with Nylon 11 or Nylon 12.

In U.S. Pat. No. 5,038,833 to Brunnhofer, a three-layer fuel line isproposed in which a tube is formed having a co-extruded outer wall ofNylon 11 or Nylon 12, an intermediate alcohol barrier wall formed froman ethylene-vinyl alcohol copolymer, and an inner water-blocking wallformed from a polyamide such as Nylon 11 or Nylon 12. In DE 40 06 870, afuel line is proposed in which an intermediate solvent barrier layer isformed of unmodified Nylon 6.6 either separately or in combination withblends of polyamide elastomers. The internal layer is also composed ofpolyamides; preferably modified or unmodified Nylon 6 while the outerlayer is composed of either Nylon 6 or Nylon 12.

Another tubing designed to be resistant to alcoholic media is disclosedin UK Application Number 2 204 376 A in which a tube is produced whichhas a thick outer layer composed of polyamides such as Nylon 6 or 6.6and/or Nylon 111 or 12 which are co-extruded with an alcohol-resistantpolyolefin, a co-polymer of propylene and maleic acid.

Heretofore it has been extremely difficult to obtain satisfactorylamination characteristics between dissimilar polymer layers. Thus allof the multi-layer tubing proposed previously has employedpolyamide-based materials in most or all of the multiple layers. Whilemany more effective solvent-resistant chemicals exist, their use in thisarea is limited due to limited elongation properties, strength andcompatibility with Nylon 11 and 12. Additionally, the previousdisclosures fail to address or appreciate the phenomenon ofelectrostatic discharge.

Electrostatic discharge can be defined as the release of electric chargebuilt up or derived from the passage of charged particles through amedium or conduit composed of essentially non-conductive materials. Theelectrostatic charge is repeatedly replenished with the passage ofadditional volumes of fuel through the conduit. Discharge repeatedlyoccurs in the same localized area gradually eroding the area and leadingto eventual rupture of the tubing. Such a rupture of the tubing can leadto the danger of fire and explosion of the flammable contents of thetubing.

Thus it would be desirable to provide a tubing material which could beemployed in motor vehicles which would be durable and prevent or reducepermeation of organic materials therethrough. It would also be desirableto provide a tubing material which would be essentially nonreactive withcomponents of the liquid being conveyed therein. Finally, it would bedesirable to provide a tubing material which would be capable ofpreventing the build-up of electrostatic discharge therein or would becapable of safely dissipating any electrostatic charge induced therein.

SUMMARY OF THE INVENTION

The present invention is a multi-layer tube for connection to a motorvehicle system to transport fluids containing hydrocarbons such as in afuel line, a vapor return line or vapor recovery line. The elongatedmulti-layer tube of the present invention includes a first layerdisposed radially innermost and having an inner surface capable ofprolonged exposure to a fluid containing hydrocarbons and an outersurface spaced a first predetermined radial thickness from the innersurface. The first layer consists essentially of an extrudable,melt-processible thermoplastic. A second layer has a secondpredetermined radial thickness equal to or less than the thickness ofthe first layer. The second layer is bonded to the outer surface of thefirst layer and consists essentially of an extrudable, melt processiblethermoplastic capable of sufficiently permanent laminar adhesion withthe outer surface of the first layer. A third layer has a thirdpredetermined radial thickness greater than the thickness of the firstlayer. The third layer has an inner face capable of sufficientlypermanent laminar adhesion to the second layer and an outer face. Thethird layer consists essentially of an extrudable, melt-processiblethermoplastic. At least one layer of the multi-layer tube is capable ofdissipating electrostatic energy in a range between about 10⁻⁴ to 10⁻⁹Ohm/cm².

DESCRIPTION OF THE DRAWINGS

The objects, features and advantages of the present invention willbecome more readily apparent from the following description, referencebeing made to the following drawings in which:

FIG. 1 is a sectional view through a piece of tubing having three layersaccording to the present invention;

FIG. 2 is a sectional view through a piece of tubing having four layersaccording to the present invention; and

FIG. 3 is a sectional view through a piece of tubing having five layersaccording to the present invention.

DESCRIPTION OF THE PREFERRED AND ALTERNATIVE EMBODIMENTS

The present invention is a multi-layer fuel line and vapor tube 10 whichcontains at least an inner or first layer 14, at least one bonding orsecond layer 16 and at least an outer or third layer 12. The tubing 10of the present invention is, preferably, fabricated by co-extrudinggiven thermoplastic materials in a conventional co-extrusion process.The tubing 10 may either be co-extruded to a suitable length or may beco-extruded in continuous length and cut to fit the given applicationsubsequently. The tubing 10 of the present invention may have an outerdiameter up to 50 mm. However, in applications such as fuel lines andvapor recovery systems, outer diameters of up to 63.5 mm (2.5 inches)are preferred.

The material may have any suitable wall thickness desired. However, inautomotive systems such as those described herein, wall thicknessesbetween 0.5 mm and 2 mm are generally employed with wall thicknesses ofapproximately 0.8 mm to approximately 1.5 mm being preferred; and wallthicknesses between about 0.8 mm and about 1.25 mm being most preferred.While it is within the scope of this invention to prepare a tubingmaterial having a plurality of overlaying layers of variousthermoplastic materials, the tubing 10 of the present inventiongenerally has a maximum of five layers inclusive of the bonding layers.In the preferred embodiment, the tubing material has three or fourlayers.

The tubing 10 of the present invention is a material which is suitablefor use in motor vehicles and comprises a relatively thick outer layerwhich is non-reactive with the external environment and can withstandvarious shocks, vibrational fatigue, and changes in temperature as wellas exposure to various corrosive or degradative compounds to which itwould be exposed through the normal course of operation of the motorvehicle. Suitable materials for use in the present invention may becomposed of any melt-processible extrudable thermoplastic material whichis resistant to ultra violet degradation, extreme changes in heat andexposure to gasoline and its additives. The material of choice may alsoexhibit resistance to environmental hazards such as exposure to zincchloride, and resistance to degradation upon contact with materials suchas engine oil and brake fluid.

It is anticipated that both the outer layer, as well as any interiorlayers bonded thereto, would be suitable for use at an outer servicetemperature range between about −40° C. and about 150° C., with a rangeof −20° C. to 120° C. being preferred. The various layers of the tubing10 are integrally laminated to one another and resistant to delaminationthroughout the lifetime of the tubing. The tubing 10 thus formed willhave a tensile strength of no less than 25 N/mm² and an elongation valueat break of at least 150%. The tubing 10 will have a burst strength at23° C. and 120° C. of at least 20 bar. The multi-layer tubing 10 of thepresent invention is sufficiently resistant to exposure to brake fluid,engine oil and peroxides such as those which may be found in gasoline.The multi-layer tube 10 has the capability of withstanding impacts of atleast 2 foot-pounds at temperatures below about −20° C. The method fordetermining impact resistance for tubing as used with respect to thepresent invention is SAE J844 (revised June 1990) paragraph 9.11 whichexpress impact resistance as foot-pounds.

The total wall thickness of the tubing 10 of the present invention isgenerally between about 0.5 mm and about 2.0 mm with a wall thicknessbetween about 0.8 mm and about 1.25 mm being preferred.

In the first, second and third embodiments of the present invention, theinner layer 14 is integrally bonded to the inner surface of the thickouter polyamide layer 12. In the present invention, the inner layer 14is a chemically dissimilar, permeation resistant, chemical resistant,fuel resistant thermoplastic material which is melt processible innormal ranges of extrusion, i.e. about 175° C. to about 250° C. By theterm “chemically dissimilar” it is meant that the inner layer 14consists essentially of a non-polyamide material which is capable ofadhesion to a bonding layer 16 interposed between the thick outer layer12 and the inner layer 14 in a manner which will be describedsubsequently.

[In each of the first, second, third and fifth embodiments, thethermoplastic material which comprises the inner layer 14 is afluoroplastic material selected from the group consisting ofpolyvinylidine fluoride, polyvinyl fluoride,polychlorotrifluoroethylene, ethylene tetrafluoroethylene copolymers, agraft copolymer of the preceding materials together with afluorine-containing polymer such as copolymers of vinylidine fluorideand chlorotrifluoroethane, and mixtures thereof.

In each of the first, second, third and fifth embodiments, the innerlayer 14 has a minimum wall thickness sufficient to achieve thepermeation resistance desired. In general, the inner layer 14 is thinnerthan the outer layer 12 with the thickness of the outer layer 12 beingbetween about 50% and about 60% of the total wall thickness of themulti-layer tubing 10. Preferably, the inner wall thickness is betweenabout 0.01 mm and about 0.2 mm with a thickness of about 0.05 mm andabout 0.2 mm being preferred and a thickness between about 0.05 mm andabout 0.17 mm being most preferred. The intermediate bonding layer 16generally may have a thickness less than or equal to that of the innerlayer 14.

The thermoplastic material employed in the inner layer 14 of the first,second, third and fifth embodiments is capable of serving as ahydrocarbon barrier to prevent significant permeation of the aromaticand aliphatic components of gasoline through to the polyamide outerlayer 12 of the tubing 10 and thus, out to the surrounding environment.

The fluoroplastic material employed in the inner layer 14 of the first,second, third and fifth embodiments of the present invention is,preferably, chemically dissimilar in structure and composition from theouter layer 12. In order to accomplish effective lamination of the twodissimilar materials, the tubing 10 of the present invention alsoincludes at least one intermediate layer 16 interposed between the twopreviously described layers and co-extruded therewith which is capableof achieving a suitable homogeneous bond between itself and the tworespective layers. The intermediate bonding layer 16 is generallycomposed of a more elastic material than that employed in the innerlayer 14.

In the first embodiment of the inner layer 14, it is preferred that thefluoroplastic material be selected from the group consisting ofpolyvinylidine fluoride, polyvinyl fluoride, and mixtures thereof. Inthe first embodiment, the thermoplastic material which comprises theinner layer 14 is, preferably, a polyvinylidine fluoroplastic derivedfrom the thermal dehalogenation of chlorodifluoroethane commerciallyavailable under the trade names “FLORAFLON” and “KYNAR” from AtochemInc. elf Aquitaine Group of Philadelphia, Pa.

In the second embodiment of the inner layer 14, it is preferred that thefluoroplastic material be selected from the group consisting ofpolychlorotrifluoroethylene, ethylene tetrafluoroethylene copolymers,and mixtures thereof. In the second embodiment of the inner layer 14,the preferred material is an ethylene tetrafluoroethylene copolymerhaving a melt temperature between about 270° C. and 560° C. and aspecific gravity of 1.7. The ethylene tetrafluoroethylene copolymeremployed herein is derived from the copolymerization of ethylene withtetrafluoroethylene. The preferred polymeric material has anethylene-derived content between about 40% and about 70% and atetrafluoroethylene content between about 30% and about 60% by totalpolymer weight with minor amounts of proprietary materials beingoptionally present. Suitable materials are commercially available underthe trade names “TEFZEL 210”, “TEFZEL 200”, and “TEFZEL 280” from E.I.duPont de Nemours, Co. of Wilmington, Del.

In the third embodiment, the thermoplastic material which comprises theinner layer 14 is a fluoroplastic material selected from the groupconsisting of polychlorotrifluoroethylene, ethylene tetrafluoroethylenecopolymers and mixtures thereof. The material employed will, preferably,have a melt temperature between about 270° C. and 560° C. and a specificgravity of 1.7. Suitable polychlorotrifluoroethylene fluoroplasticmaterials may be derived from the pyrolysis of chlorodifluoromethane. Itis believed that suitable ethylene tetrafluoroethylene copolymersbroadly have ethylene-derived contents between about 40% and about 70%;tetrafluoroethylene contents between about 30% and about 60% by totalpolymer weight; and minor amounts of proprietary materials. Suitablematerials are commercially available under the tradenames “TEFZEL 210”,“TEFZEL 200”, and “TEFZEL 280” from E.I. duPont de Nemours, Co. ofWilmington, Del.

In the fourth embodiment, the thermoplastic material employed in theinner layer 14 of the present invention is a melt-processible extrudablethermoplastic material resistant to extreme changes in heat and exposureto chemical components such as are found in engine oil and brake fluid.The thermoplastic material of choice is, preferably, a chemicallysimilar material in structure and composition to the thermoplasticmaterial employed in the thick outer layer 12. As used herein, the term“chemically similar material” is defined as a thermoplastic materialselected from the group consisting of 12 carbon block polyamides, 11carbon block polyamides, zinc chloride resistant 6 carbon blockpolyamides, thermoplastic elastomers, and mixtures thereof. Thethermoplastic elastomers which can successfully be employed in thetubing 10 of the present invention are commercially available undertradenames such as: SANTOPRENE®, a thermoplastic rubber commerciallyavailable from Advanced Elastomer Systems of St. Louis, Mo.; KRATON®, athermoplastic rubber composed of a styrene-ethylene/butylene-styreneblock copolymer commercially available from Shell Chemical Co. ofHouston, Tex.; SARLINK, an oil resistant thermoplastic commerciallyavailable from Novacor Chemicals of Leominster, Mass.; and VICHEM, afamily of polyvinyl chloride compounds commercially available fromVichem Corporation of Allendale, Mich.

The thermoplastic material employed in the inner layer 14 of the fourthembodiment of the tubing 10 either may be identical to the materialemployed in the thick outer layer 12 or may be a different thermoplasticselected from those listed to take advantage of specific properties ofthe various thermoplastics. In the preferred embodiment, the inner layer14 is composed of a material similar to or identical to the thick outerlayer 12. In the preferred embodiment, a polyamide such as Nylon 12 canbe effectively employed.

The thermoplastic employed in the inner layer 14 of the fourthembodiment may be either modified or unmodified. If modified, it isanticipated that the material will contain various plasticizers as arereadily known in the art. In the preferred embodiment, the polyamidewill contain up to 17% by composition weight plasticizer; with amountsbetween about 1% and about 13% being preferred.

The inner layer 14 of the fourth embodiment may have a thicknesssufficient to supply strength and chemical resistance properties to themulti-layer tubing. Specifically, the inner layer 14 is of sufficientthickness to impede permeation of aliphatic and aromatic hydrocarbonmolecules and migration of those molecules through to the thick outerlayer. In the present invention, the inner layer has a wall thicknessless than that of the thick outer layer. In the preferred embodiment,the inner layer has a wall thickness between about 10% and 25% that ofthe outer layer; preferably less than between about 0.05 mm and about0.4 mm; with a wall thickness between about 0.1 mm and about 0.3 mmbeing preferred.

In order to accomplish effective lamination of the two thermoplasticmaterials which compose the inner and outer layers of the fourthembodiment, the tubing of the present invention also includes at leastone intermediate layer 16 interposed between the two previouslydescribed layers and co-extruded therewith which is capable of achievinga suitable homogeneous bond between itself and the two respectivelayers. The intermediate bonding layer 16 is generally composed of amore elastic material than that employed in the inner layer 14.

In the fifth embodiment, the inner or first layer 14 is integrallybonded to the thick polyamide outer or third layer 12 by means of theintermediate bonding or second layer 16. In the present invention, theinner layer 14 is a chemically dissimilar permeation resistant, chemicalresistant, fuel resistant thermoplastic material which ismelt-processible in normal ranges of extrusion, i.e. about 175° C. toabout 250° C. By the term “chemically dissimilar” it is meant that theinner layer 14 is a non-polyamide material which is capable of adhesionto the intermediate bonding layer 16 interposed between the thick outerlayer 12 and the inner layer 14.

In the fifth embodiment, the thermoplastic material which comprises theinner layer 14 is selected from the group consisting of polyvinylidinefluoride, polyvinyl fluoride, and mixtures thereof. The material canalso be a graft copolymer of the preceding materials together with afluorine-containing polymer such as copolymers of vinylidine fluorideand chlorotrifluoroethane. Suitable material employed would containbetween about 60% and about 80% by weight polyvinylidine difluoride.Materials so formed have a melting point between about 200° C. and about220° C. and a molding temperature between about 210° C. and about 230°C.

The inner layer 14 of the present invention according to the fifthembodiment, as illustrated in FIG. 3, may include an innermostelectrostatic dissipation sub-layer 22 which is also capable of servingas a hydrocarbon barrier to assist in the prevention of permeation ofaromatic and aliphatic compounds found in gasoline through to the outerlayer 12 of the tubing 10 and, thus, out to the surrounding environment.

In the fifth embodiment, the electrostatic dissipation sub-layer 22 ofthe inner layer 14 may be integrally bonded to the inner surface of anoptional sub-layer 20 disposed between sub-layer 22 and the intermediatebonding layer 16. Preferably, the sub-layers 20 and 22 are chemicallysimilar materials in structure and composition. As used here, the term“chemically similar material” is defined as a thermoplastic materialselected from the group consisting of polyvinylidine fluoride, polyvinylfluoride, a graft copolymer of the preceding materials together with afluorine-containing polymer such as copolymers of vinylidine fluorideand chlorotrifluoroethane, a copolymer of a vinyl fluoride andchlorotrifluoroethylene, the vinyl fluoride material selected from thegroup consisting of polyvinylidine fluoride, polyvinyl fluoride, andmixtures thereof; a copolymer of vinyl fluoride material and ethylenetetrafluoroethylene; and a non-fluorinated elastomer, and mixturesthereof. Preferably, the sub-layers 20 and 22 are composed of the samematerial, with the exception of the electrostatic dissipation sub-layer22 including additional conductive material as described hereinafter.The sub-layers 20 and 22, intermediate bonding layer 16, outer layer 12and jacket 18 define a five layer tubing 10. In the present invention,the inner layer 14 is composed of a thermoplastic material chemicallydissimilar to the thermoplastic material employed in the outer layer 12which is melt-processible in the normal ranges of extrusion, i.e. about175° C. to about 250° C. The thermoplastic material employed in theinner layer 14 is capable of sufficiently permanent laminar adhesion tothe intermediate bonding layer 16.

In the fifth embodiment, the thermoplastic material which comprises theelectrostatic dissipation sub-layer 22 of the inner layer 14 consistsessentially of: a copolymer of a vinyl fluoride andchlorotrifluoroethylene, the vinyl fluoride material selected from thegroup consisting of polyvinylidine fluoride, polyvinyl fluoride, andmixtures thereof; a copolymer of vinyl fluoride material and ethylenetetrafluoroethylene; and a non-fluorinated elastomer. The thermoplasticmaterial employed in the present invention, preferably contains betweenabout 10% and about 18% by weight of a vinylidinefluoride-chlorotrifluoroethylene copolymer which itself has a vinylidinefluoride content between about 40% and 60% by copolymer weight. Thematerial also, preferably contains between about 50% and about 70% byweight of a vinylidine fluoride-tetrafluoroethylene copolymer. Thenon-fluorinated elastomer is selected from the group consisting ofpolyurethanes, and mixtures thereof. In the fifth embodiment, thematerial contains between about 10% and about 25% by weightpolyurethane.

The material according to the fifth embodiment, also contains conductivemedia in quantities sufficient to permit electrostatic dissipation in adesired range. In the fifth embodiment, the electrostatic dissipationsub-layer 22 of the inner layer 14 exhibits electrostatic conductivecharacteristics capable of dissipating electrostatic charges in therange of 10⁻⁴ to 10⁻⁹ Ohm/cm². Suitable material is commerciallyavailable under the trade name XPV-504KRC CEFRAL SOFT CONDUCTIVE.

In the fifth embodiment, the electrostatic dissipation sub-layer 22 ofthe inner layer 14 is maintained at thicknesses suitable for achievingstatic dissipation and suitable laminar adhesion respectively; generallybetween about 10% and 20% of the thick outer layer 12. The thickness ofthe electrostatic dissipation sub-layer 22 of the inner layer 14 ispreferably between about 0.1 mm and about 0.2 mm. The intermediatebonding layer 16 preferably has a thickness approximately equal to thethickness of the electrostatic dissipation sub-layer 22, preferablybetween about 0.05 mm and about 0.15 mm.

In the fifth embodiment, the inner layer 14 is maintained at a thicknesssuitable to achieve a hydrocarbon permeation value for the tubing 10 ofthe present invention no greater than about 0.5 g/m² in a 24 hourinterval. To accomplish this, the characteristics of the inner layer 14can be relied upon solely or in concert with the intermediate bondinglayer 16. It is anticipated that the thickness of the inner layer 14 andthe intermediate bonding layer 16 can be modified to accomplish thisend. In the fifth embodiment, the inner layer 14 has a thickness betweenabout 10% and about 20% of the thick outer layer 12. In the fifthembodiment, the inner layer 14 has a thickness between about 0.15 mm andabout 0.25 mm with a thickness of about 0.18 mm to about 0.22 mm beingpreferred. The intermediate bonding layer 16 is maintained at athickness sufficient to permit sufficient laminar adhesion between theouter layer 12 and inner layer 14. The intermediate bonding layer 16generally has a thickness less than that of the inner layer 14. Thethickness of the intermediate bonding layer 16 is, preferably, betweenabout 0.05 mm and about 0.1 mm.

In the sixth embodiment, the inner layer 14 is composed of a polyamidethermoplastic derived from the condensation polymerization ofcaprolactam. Such materials are commonly referred to as a 6-carbon blockpolyamide or Nylon 6. In the sixth embodiment of the inner layer 14, the6-carbon block polyamide either inherently exhibits zinc chlorideresistance or contains sufficient quantities of modifying agents toimpart a level of zinc chloride resistance greater than or equal to thatrequired by Performance Requirement 9.6 as outlined in SAE StandardJ844, i.e. non-reactivity after 200 hour immersion in a 50% by weightzinc chloride solution. The Nylon 6 which composes the inner layer 14 ofthe tubing 10 of the sixth embodiment can also be modified with variousplasticizers, flame retardants and the like in manners which would beknown to one reasonably skilled in the art. In the sixth embodiment, the6-carbon block polyamide material is preferably a multi-component systemcomprised of a Nylon-6 copolymer blended with other Nylons and olefiniccompounds. The zinc chloride resistant Nylon-6 of choice will have amelt temperature between about 220° C. and 240° C. Examples ofthermoplastic materials suitable for use in the tubing 10 of the presentinvention are materials which can be obtained commercially under thetrade names M-7551 from NYCOA Corporation and ALLIED 1779 from AlliedChemical.

In the sixth embodiment of the inner layer 14, the 6-carbon blockpolyamide may, optionally, include other modifying agents such asvarious plasticizing agents generally present in amounts between about1.0% and about 13% by total weight of the thermoplastic composition asare readily known in the art. The polyamide material employed,preferably, is an impact-modified material capable of withstandingimpacts of at least 2 foot-pounds at temperatures below about −20° C.

In the sixth embodiment, the inner layer 14 has the minimum wallthickness sufficient to achieve the permeation resistance desired. Ingeneral, the inner layer 14 is thinner than the outer layer 12 with thethickness of the outer layer 12 being between about 50% and about 60% ofthe total wall thickness of the tubing 10 or between 55% and 60% of thethickness of the thick outer layer 12. In the specified embodiment, theinner layer 14 wall thickness is between about 0.01 mm and about 0.2 mmwith a thickness of about 0.05 mm to about 0.17 mm being preferred. Theintermediate bonding layer 16 generally may have a thickness less thanor equal to that of the inner layer 14.

In any of the embodiments disclosed, at least one layer, preferably theinner layer 14 and/or the intermediate bonding layer 16, may exhibitconductive characteristics rendering it capable of dissipation ofelectrostatic charge in the range of 10⁻⁴ to 10⁻⁹ Ohm/cm². Thefluoroplastic material employed in the conductive layer of the presentinvention may be inherently conductive in these ranges or, preferably,includes in its composition a conductive media in sufficient quantity topermit electrostatic dissipation in the range defined. The conductivemedia may be any suitable material of a composition and shape capable ofeffecting this static dissipation. The conductive material may beselected from the group consisting of elemental carbon, stainless steel,highly conductive metals such as copper, silver, gold, nickel andsilicon, and mixtures thereof. The term “elemental carbon” as usedherein is employed to describe and include materials commonly referredto as “carbon black”. The carbon black can be present in the form ofcarbon fibers, powders, spheres, and the like.

The amount of conductive material contained in the fluoroplastic isgenerally limited by considerations of low temperature durability andresistance to the degradative effects of the gasoline or fuel passingthrough the tubing 10. In the preferred embodiment, the fluoroplasticmaterial contains conductive material in an amount sufficient to effectelectrostatic dissipation. However, the maximum amount employed thereinis less than 5% by volume with a concentration between about 2% andabout 4% being preferred.

The conductive material can either be blended into the melt-processiblefluoroplastic material so as to be interstitially integrated into thecrystalline structure of the polymer or can be incorporated duringpolymerization of the monomers that make up the fluoroplastic material.Without being bound to any theory, it is believed that carbon-containingmaterials such as carbon black may be incorporated duringco-polymerization of the surrounding fluoroplastic material. Materialsuch as stainless steel are more likely to be blended into thecrystalline structure of the polymer.

In each of the embodiments, the intermediate bonding layer 16 iscomposed of a thermoplastic material which also exhibits properties ofresistance to permeation of aliphatic and aromatic materials such asthose found in fuel. The thermoplastic material employed herein ispreferably a melt-processible co-extrudable thermoplastic which may ormay not contain various plasticizers and other modifying agents.

The intermediate bonding layer 16, in addition to permitting ahomogeneous bond between the inner layer 14 and outer layer 12, andexhibiting resistance to permeation of fuel components, also may exhibitconductive or static dissipative characteristics such as those describedpreviously. Thus, the intermediate bonding layer 16 may optionallyinclude sufficient amounts of conductive media to effect electrostaticdissipation in the range of 10⁻⁴ to 10⁻⁹ Ohm/cm². As with the innerlayer 14, the intermediate bonding layer 16 may be inherentlyelectrostatically dissipative or may be rendered so by the inclusion ofcertain conductive material such as those selected from the groupconsisting of elemental carbon, stainless steel, copper, silver, gold,nickel, silicon and mixtures thereof.

It is preferred that the inner layer 14 and the bonding layer 16 bemaintained at the minimum thickness necessary to prevent permeation ofthe fuel through the tubing material. It is preferred that the amount ofhydrocarbon permeation through the tubing 10 be no greater than 0.5gm/m² in a 24 hour interval. The thickness of the inner layer 14 can bevaried to accomplish this end.

The intermediate bonding layer 16 is of sufficient thickness to permitan essentially homogeneous bond between the inner layer 14 and outerlayer 12. In general, the intermediate bonding layer 16 can be thinnerthan the other two layers and can constitute between about 10% and about20% of the total wall thickness of the multi-layer tube 10. In thepreferred embodiment, the thickness of the intermediate bonding layer 16is between about 0.01 mm and about 0.2 mm with a thickness between about0.05 mm and about 0.2 mm being preferred; and a thickness between about0.05 mm and about 0.15 mm being most preferred.

In the first, second and third embodiments of the present invention, theintermediate bonding layer 16 consists essentially of a fluoroplasticmaterial selected from the group consisting of polyvinylidine fluoride,polyvinyl fluoride, polyvinyl acetate-urethane blends, and mixturesthereof. One preferred fluoroplastic material is a polyvinylidinederived from the thermal dehalogenation of chlorodifluoroethane. Onepreferred non-fluorocarbon material is a polyvinyl acetate/urethaneblend. The material of choice exhibits an affinity to polymers employedin the outer layer such as Nylon 12 or Nylon 6. Suitable fluoroplasticmaterials are commercially available under the trade name “ADEFLON A”;while suitable non-fluoroplastic materials are commercially availableunder the tradename “ADEFLON D” both from Atochem Inc. elf AquitaineGroup of Philadelphia, Pa.

In the fourth embodiment of the present invention, the intermediatebonding layer 16 is a chemically dissimilar, permeation resistant,chemical resistant, fuel resistant thermoplastic material which is meltprocessible in normal ranges of extrusion, i.e. about 175° C. to about250° C. By the term “chemically dissimilar” it is meant that theintermediate bonding layer 16 is a non-polyamide material which iscapable of integral adhesion with and between the thick outer layer 12and the inner layer 14 as a result of co-extrusion.

In the fourth embodiment, the thermoplastic material which comprises theintermediate bonding layer 16 is a thermoplastic polyester derived fromethylene glycol selected from the group consisting of polybutyleneterephthalate, polyethylene terephthalate, polyteremethyleneterephthalate, and mixtures thereof. The preferred material ispolybutylene terephthalate. Suitable material is commercially availableunder the trade name 1607 ZE40 from Hüls of Dusseldorf, Germany.

In the fifth embodiment, the intermediate bonding layer 16 is composedof a thermoplastic material which may exhibit properties of resistanceto the permeation of aliphatic and aromatic materials such as thosefound in fuel in addition to exhibiting suitable bondingcharacteristics. The thermoplastic material employed herein ispreferably a melt-processible co-extrudable fluoroplastic blend whichwill exhibit an infinity to conventional polymers such as Nylon 12, andmay optionally contain various plasticizers and other modifying agents.In the fifth embodiment, the fluoroplastic which comprises theintermediate bonding layer 16 consists essentially of: a polyvinylfluoride compound selected from the group consisting of polyvinylidinefluoride polymers, polyvinyl fluoride polymers, and mixtures thereof; avinylidine fluoride-chlorotrifluoroethylene copolymer; and a polyamidematerial selected from the group consisting of 12 carbon blockpolyamides, 11 carbon block polyamides, 6 carbon block polyamides, andmixtures thereof. The vinylidine fluoride-chlorotrifluoroethylenecopolymer preferably, contains between about 60% and about 80% by weightpolyvinylidine difluoride. In the fifth embodiment, the intermediatebonding layer 16 consists essentially of between about 35% and about 45%by weight of a copolymer of vinylidine fluoride andchlorotrifluoroethylene; between 25% and about 35% by weightpolyvinylidine fluoride; and between about 25% and about 35% by weightof a polyamide selected from the group consisting of 12 carbon blockpolyamides, 11 carbon block polyamides, and mixtures thereof. One suchpolymeric material suitable for use in the multi-layer tubing 10 of thepresent invention is commercially available from Central Glass of UbeCity, Japan under the trade designation CEFRAL SOFT XUA-2U. Thismaterial is a graft copolymer of a fluorine-containing elastomericpolymer with a fluorine-containing crystalline polymer. The elastomericpolymer is, preferably, a material copolymerized from an alkyldifluoride selected from the group consisting of vinyl difluoride,vinylidine difluoride, and mixtures thereof, and a chlorofluoroalkeneselected from the group consisting of ethylene chlorotrifluoroethylene.The crystalline polymer is preferably a haloalkene such as ethylenechlorotrifluoroethylene.

In the fifth embodiment, the bonding layer 16 is the product of thecopolymerization of ethylene chlorotrifluoroethylene and a vinylidinedifluoride chlorotrifluoroethylene copolymer having a melting pointbetween about 180° C. and about 210° C. and a molding temperaturebetween about 230° C. and about 260° C.

In the sixth embodiment, the intermediate bonding layer 16 is integrallybonded to the inner surface of the thick outer polyamide layer 12. Inthe present invention, the intermediate bonding layer 16 is a chemicallydissimilar permeation resistant, chemical resistant, fuel resistantthermoplastic material which is melt processible in normal ranges ofextrusion, i.e. about 175° C. to about 250° C. By the term “chemicallydissimilar” it is meant that the intermediate bonding layer 16 consistsessentially of a non-polyamide material which is capable of adhesion toact as a bonding agent interposed between the thick outer layer 12 andthe inner layer 14 in a manner which will be described subsequently.

In the sixth embodiment, the thermoplastic material which comprises theintermediate bonding layer 16 is a thermoplastic material selected fromthe group consisting of co-polymers of substituted or unsubstitutedalkenes having less than four carbon atoms and vinyl alcohol, alkeneshaving less than four carbon atoms and vinyl acetate, and mixturesthereof. In the sixth embodiment, the thermoplastic material employedwill be resistant to permeation by and interaction with short chainaromatic and aliphatic compounds such as those which would be found ingasoline.

In the sixth embodiment, the preferred material is a copolymer ofethylene and vinyl alcohol which has an ethylene content between about27% and about 35% by weight with an ethylene content between about 27%and about 32% being preferred. Examples of suitable materials which canbe employed in the tubing of the present invention include: ethylenevinyl alcohol commercially available from EVA/LA.

The intermediate bonding layer 16 of the sixth embodiment serves to bondthe thick outer layer 12 to the inner layer 14 to form a secure laminarbond therebetween. The inner layer 14 provides a stable fuel-contactingsurface on the interior of the tube 10. The intermediate bonding layer16 is of sufficient thickness to permit an essentially homogeneous bondbetween the inner layer 14 and outer layer 12. In general, theintermediate bonding layer 16 can be thinner than the other layers andcan constitute between about 10% and about 50% of the total wallthickness or between about 20% and about 30% of the thickness of theouter layer 12. In the specified embodiment, the thickness of theintermediate bonding layer 16 is between about 0.01 mm and about 0.25 mmwith a thickness between about 0.05 mm and about 0.20 mm beingpreferred.

The thermoplastic material employed in the intermediate bonding layer 16of the sixth embodiment is capable of serving as a hydrocarbon barrierto prevent significant permeation of the aromatic and aliphaticcomponents of gasoline through to the polyamide outer layer 12 of thetubing 10 and thus, out to the surrounding environment. Theeffectiveness of the barrier layer at preventing such permeation willvary depending on numerous factors including but not limited to thethickness and composition of the inner layer 14, the thickness of thebonding layer 16 and the composition of the materials conveyed throughthe tubing 10. In the sixth embodiment, it is anticipated that thebonding layer 16 will be capable of providing the tubing 10 of thepresent invention with a passive hydrocarbon permeation level less thanabout 0.5 g/m² per 24 hour.

In each of the embodiments, the outer layer 12 has a wall thicknesssufficient to provide suitable strength and endurance to the multi-layertubing 10 of the present invention. Generally, in applications involvingautomotive vehicles, the outer layer 12 comprises between about 50% andabout 70% of the total wall thickness. In general, the outer layer 12has a wall thickness between about 0.6 mm and about 0.9 mm; with apreferred wall thickness between about 0.7 mm and about 0.8 mm, and amost preferred wall thickness between about 0.7 mm and about 0.75 mm. Asindicated previously, the material can be extruded by conventionalco-extrusion methods to any continuous length desired.

In general, the outer layer 12 may be composed of any melt-processibleextrudable thermoplastic material which is resistant to ultravioletdegradation, extreme changes in heat, exposure to environmental hazardssuch as zinc chloride, and degradation upon contact with engine oil andbrake fluid.

In the first, second, fourth and fifth embodiments, the outer layer 12is selected from the group consisting of 12 carbon block polyamides, 11carbon block polyamides, zinc chloride resistant 6 carbon blockpolyamides, thermoplastic elastomers, and mixtures thereof. Thethermoplastic elastomers are commercially available under trade namessuch as: SANTOPRENE®, a thermoplastic rubber commercially available fromAdvanced Elastomer Systems of St. Louis, Mo.; KRATON®, a thermoplasticrubber composed of a styrene-ethylene/butylene-styrene block copolymercommercially available from Shell Chemical Co. of Houston, Tex.;SARLINK, an oil resistant thermoplastic commercially available fromNovacor Chemicals of Leominster, Mass.; and VICHEM, a family ofpolyvinyl chloride compounds commercially available from VichemCorporation of Allendale, Mich. These materials which compose the outerlayer can be present in their unmodified state or can be modified withvarious plasticizers, flame retardants and the like in manners whichwould be known to one reasonably skilled in the art. The thermoplasticmaterial of choice has an elongation value at break of at least 150% andan ability to withstand impacts of at least 2 foot-pounds attemperatures below about −20° C.

In the first, second, fourth and fifth embodiments, a polyamide such asNylon 12 can be effectively employed. It is anticipated that the Nylon12 may be either modified or unmodified. If modified, it is anticipatedthat the material will contain various plasticizers as are readily knownin the art. Preferably, the polyamide will contain up to 17% bycomposition weight plasticizer; with amounts between about 1% and about13% being preferred. The polyamide material employed, preferably, is animpact-modified material capable of withstanding impacts of 2foot-pounds at temperatures below about −20° C.

In the first, second, fourth and fifth embodiments, the outer layer 12has a wall thickness sufficient to provide suitable strength andendurance to the multi-layer tubing 10 of the present invention. Inapplications involving automotive vehicles, the outer layer 12 comprisesbetween about 50% and about 70% of the total wall thickness. In general,the outer layer 12 has a wall thickness between about 0.6 mm and about0.9 mm; with a preferred wall thickness between about 0.7 mm and about0.8 mm, and a most preferred wall thickness between about 0.7 mm andabout 0.75 mm. In the fourth embodiment, the outer layer 12, preferably,has a wall thickness between about 0.5 mm and about 1.0 mm with apreferred range being between about 0.6 mm and about 0.8 mm. In thefifth embodiment, the Nylon 12 outer layer 12 preferably has a wallthickness between about 0.5 mm and about 0.8 mm with a preferred rangebeing between about 0.6 mm and about 0.75 mm. As indicated previously,the material is extruded by conventional co-extrusion methods to anycontinuous length desired. As indicated previously, the material can beextruded by conventional co-extrusion methods to any continuous lengthdesired.

In the third and sixth embodiments, the outer layer 12 is composed of apolyamide thermoplastic derived from the condensation polymerization ofcaprolactam. Such materials are commonly referred to as a 6-carbon blockpolyamide or Nylon 6. In this third and sixth embodiments, the 6-carbonblock polyamide either inherently exhibits zinc chloride resistance orcontains sufficient quantities of modifying agents to impart a level ofzinc chloride resistance greater than or equal to that required byPerformance Requirement 9.6 as outlined in SAE Standard J844, i.e.non-reactivity after 200 hour immersion in a 50% by weight zinc chloridesolution. The Nylon 6 which composes the outer layer 12 of the tubing 10of these embodiments can also be modified with various plasticizers,flame retardants and the like in manners which would be known to onereasonably skilled in the art. In these embodiments, the 6-carbon blockpolyamide material is preferably a multi-component system comprised of aNylon-6 copolymer blended with other Nylons and olefinic compounds. Thezinc chloride resistant Nylon-6 of choice will have a melt temperaturebetween about 220° C. and 240° C. Examples of thermoplastic materialssuitable for use in the tubing 10 of the present invention are materialswhich can be obtained commercially under the trade names M-7551 fromNYCOA Corporation and ALLED 1779 from Allied Chemical.

In the third and sixth embodiments, the 6-carbon block polyamide may,optionally, include other modifying agents such as various plasticizingagents generally present in amounts between about 1.0% and about 13% bytotal weight of the thermoplastic composition as are readily known inthe art. The polyamide material employed, preferably, is animpact-modified material capable of withstanding impacts of at least 2foot-pounds at temperatures below about −20° C.

In the third and sixth embodiments, the outer layer 12 has a wallthickness sufficient to provide suitable strength and endurance to themulti-layer tubing of the present invention. In applications involvingautomotive vehicles, the outer layer 12 comprises between about 50% andabout 60% of the total wall thickness. In general, the outer layer has awall thickness between about 0.5 mm and about 0.8 mm; with a preferredwall thickness between about 0.6 mm and about 0.7 mm. As indicatedpreviously, the material can be extruded by conventional co-extrusionmethods to any continuous length desired.

In any of the disclosed embodiments, the tubing 10 of the presentinvention may also, optionally include an outer jacket or fourth layer18 which surrounds the outer or third layer 12. The jacket 18 may beeither co-extruded with the other layers during the extrusion process ormay be put on in a subsequent process such as cross-extrusion. The outerjacket 18 may be made of any material chosen for its structural orinsulating characteristics and may be of any suitable wall thickness. Inthe preferred embodiment, the outer jacket 18 may be made of athermoplastic material selected from the group consisting ofzinc-chloride resistant Nylon 6, Nylon 11, Nylon 12, polypropylene, andthermoplastic elastomers such as: SANTOPRENE®, a thermoplastic rubbercomposition commercially available from Advanced Elastomer Systems ofSt. Louis, Mo.; KRATON®, a thermoplastic rubber composition composed ofa styrene-ethylene/butylene-styrene block copolymer commerciallyavailable from Shell Chemical Co. of Houston, Tex.; VICHEM, a family ofpolyvinyl chloride compounds commercially available from VichemCorporation of Allendale, Mich.; and SARLINK, an oil resistantthermoplastic composition commercially available from Novacor Chemicalsof Leominster, Mass. If desired, these materials may be modified toinclude flame retardants, plasticizers and the like.

In the fourth embodiment of the invention, the outer jacket may,preferably, exhibit conductive characteristics in that it is capable ofdissipation of electrostatic charge in the range of 10⁻⁴ to 10⁻⁹Ohm/cm². The material which composes the outer jacket may be inherentlyconductive in these ranges or, preferably, include in its composition aconductive media in sufficient quantity to permit electrostaticdissipation in the range defined. The conductive media may be anysuitable material of a composition and shape capable of effecting thisstatic dissipation. The conductive material may be selected from thegroup consisting of elemental carbon, stainless steel, highly conductivemetals such as copper, silver, gold, nickel and silicon, and mixturesthereof. The term “elemental carbon” as used herein is employed todescribe and include materials commonly referred to as “carbon black”.The carbon black can be present in the form of carbon fibers, powders,spheres, and the like.

The amount of conductive material contained in the outer jacket isgenerally limited by considerations of low temperature durability andresistance to the degradative effects of the gasoline or fuel passingthrough the tubing. In the fourth embodiment, the thermoplastic materialcontains conductive material in an amount sufficient to effectelectrostatic dissipation. However, the maximum amount employed thereinis preferably less than 5% by volume.

The conductive material can either be blended into the crystallinestructure of the polymer or can be incorporated during polymerization ofmonomers that make up the polymer. Without being bound to any theory, itis believed that carbon-containing materials such as carbon black may besubject to incorporation into the monomer that produces the surroundingthermoplastic material. Materials such as stainless steel are morelikely to be blended into the crystalline structure of the polymer.

The following is a brief description of the various exemplary,commercially available compounds described hereinabove. It is to beunderstood that these are examples of suitable compounds forillustrative purposes. Thus, it is to be further understood that othersuitable compounds are contemplated and are within the scope of thepresent invention.

SANTOPRENE®, commercially available from Advanced Elastomer Systems, L.P. of St. Louis, Mo. is a thermoplastic rubber FR grade. Aside from thethermoplastic rubber, it also contains antimony trioxide flameretardant, and may contain carbon black, CAS No. 1333-86-4. SANTOPRENE®thermoplastic rubber may react with strong oxidizing chemicals, and alsoreacts with acetal resins at temperatures of 425° F. and above,producing decomposition of the acetal resins, and formaldehyde as adecomposition product. Decomposition of halogenated polymers andphenolic resins may also be accelerated when they are in contact withSANTOPRENE® thermoplastic rubber at processing temperatures. Physicalcharacteristics of SANTOPRENE® include a slightly rubber-like odor, andthe appearance of black or natural (colorable) pellets. It is thermallystable to 500° F. The flash ignition temperature is greater than 650° F.by method ASTM-D 1929-77, and by the same method, self-ignitiontemperature is above 700° F. The typical specific gravity is 0.90 to1.28. The material has various hardnesses which are suitable in thepresent invention, however, in the preferred embodiment, the SANTOPRENE®thermoplastic rubber having an 80 Shore A hardness is utilized. TheSANTOPRENE® thermoplastic rubber is designed to offer fluid and oilresistance equivalent to that of conventional thermoset rubbers such asneoprene. The resistance of the SANTOPRENE® rubber grades to oils can beclassified by using the SAE J200/ASTM D2000 standard classificationsystem for rubber.

ADEFLON A is a polyvinylidene fluoride commercially available fromAtochem Inc. elf Aquitaine Group of Philadelphia, Pa. Its typical use isas a binding material for polyamides/polyvinylidene fluoride. Theproduct is stable under normal use conditions, and above 230° C., thereis a release of monomer traces. Physical properties include: at 20° C.the material is a granulated solid having a white/slightly yellow colorand no odor. The crystal melting point is 175° C., and beginning ofdecomposition is 230° C. In water at 20° C., the product is non-soluble.The density at 20° C. bulk is 1 to 1.1 g/cm³.

The Vichem Corporation vinyl compounds are polyvinyl chloride compoundscomposed of a vinyl resin and functioning additives. The ingredientsinclude a stabilizer, a resin CAS No. 75-01-4, a plasticizer CAS No.68515-49-1, an epoxy soya oil CAS No. 8013-07-8, a filler CAS No.1317-65-3 and carbon black CAS No. 1333-85-4. The specific gravity is1.35 and the compound has the appearance of pellets and has acharacteristically bland odor.

KRATON®, commercially available from Shell Chemical Co. of Houston,Tex., is a thermoplastic rubber having a specific gravity of 0.90 to1.90 and a hardness of 15A to 60D. The tensile strength is up to 2,500psi. The elongation is up to 750% and the tear strength is up to 750 pli(130 kN/m). The flex modulus is 750 to 100,000 psi. The servicetemperature is −70° C. to 150° C. The ozone resistance is excellent, UVresistance is excellent, fluid resistance is fair to excellent, andflame resistance is fair to excellent.

SARLINK is a thermoplastic elastomer commercially available from NovacorChemicals Inc. of Leominster, Mass. The specific gravity ranges from1.13 to 1.22. The modulus at 100% ranges between 260 and 570 psi. Thetensile strength ranges between 780 and 2,060 psi. The ultimateelongation ranges between about 345 and about 395%. The tear strengthranges between about 81 and about 196 pli. The tension set rangesbetween about 4 and 6%. It has excellent fluid resistance to acids andalkalis, aqueous solutions, organic solvents, petroleum oils and fuels,automotive fluids such as automatic transmission, power steering, etc.and industrial fluids. It has fair fluid resistance to automotive fluidssuch as hydraulic brake, lithium grease, antifreeze, etc. and poorresistance to organic solvents. The SARLINK product is a solid, blackpellet material with a mildly pungent odor. It is insoluble in water at20° C.

KYNAR, commercially available from Atochem Inc. elf Aquitaine Group ofPhiladelphia, Pa., is a vinylidene fluoride-hexafluoropropylenecopolymer. Its chemical name is 1-propene,1,1,2,3,3,3-hexafluoro-1,1-difluoroethene polymer. Its melting point is155°-160° C. Its specific gravity is 1.77-1.79 at 23° C. It appearstranslucent and has no odor.

A suitably conductive KYNAR material, known as KYNAR RC 10,098 is alsocommercially available from Atochem Inc. elf Aquitaine Group ofPhiladelphia, Pa. This compound is identified as ahexafluoropropylene-vinylidine fluoride copolymer, CAS No. 9011-17-0.The melting point is between about 155° C. and about 160° C. It is notsoluble in water. It appears as translucent pellets having no odor. Itis stable under 300° C.

CEFRAL SOFT XUA-2U, commercially available from Central Glass Company,Ltd., Chiyodaku, Tokyo, Japan is a copolymer containing 40% vinylidenefluoride-chlorotrifluoroethylene copolymer, 30% polyvinylidene fluorideand 30% Nylon 12. The material has a specific gravity of 1.45 at 23° C.,a melting point of 173° C. and a mold temperature of 220° F. Thematerial has an elongation at break of 478% and a tensile strength of430 Kgf/cm².

XPV-504 KRC CEFRAL SOFT CONDUCTIVE is commercially available fromCentral Glass Company, Ltd., Chiyodaku, Tokyo, Japan and is a polymericcomposition containing 14% vinylidene fluoride-chlorotrifluoroethylenecopolymer; 63% vinylidene fluoride-tetrafluoroethylene copolymer; 20%polyurethane elastomer; and 3% carbon black. The material has a meltpoint of 165° C. and a specific gravity of 1.80 at 23° C.

TEFZEL is commercially available from DuPont Polymers, Specialty PolymerDivision, Wilmington, Del. The material designates a family of ethylenetetrafluoroethylene fluoropolymers having various commercial grades. Thematerial has a melting point between 255° C. and 280° C. as determinedby ASTM method DTA D3418. The specific gravity for the material isbetween 1.70 and 1.72 as determined by ASTM method D792. Impact strengthfor the material at −65° F. is between 2.0 ft-lbs/inch and 3.5ft-lbs/inch as determined by ASTM method D256, commonly referred to asNotched Izod Impact Strength. The hardness durometer as determined byASTM method D2240 for all grades of TEFZEL is D70. Tensile strength at73° F. is between 5,500 psi and 7,000 psi. TEFZEL was first introducedin 1970 having outstanding mechanical strength, high temperature andcorrosion resistance. The material is available in three productiongrades, TEFZEL 200, TEFZEL 210 and TEFZEL 280 which can be applied inthe present invention. Ultimate elongation at break is between 150% and300%, depending on the grade as determined by ASTM method D638.

In summary, the first embodiment of the multi-layer tubing 10 comprisesan outer layer 12 consisting essentially of a thermoplastic materialselected from the group consisting of 12 carbon block polyamides, 11carbon block polyamides, thermoplastic elastomers, and mixtures thereof;an inner layer 14 consisting essentially of a thermoplastic materialselected from the group consisting of polyvinylidine fluoride, polyvinylfluoride, and mixtures thereof; and an intermediate bonding layer 16consisting essentially of an extrudable thermoplastic capable ofsufficiently permanent laminar adhesion to the polyamide outer layer 12selected from the group consisting of polyvinylidine fluoride, polyvinylfluoride, and mixtures thereof.

In summary, the second embodiment of the multi-layer tubing 10 comprisesan outer layer 12 consisting essentially of a thermoplastic materialselected from the group consisting of 12 carbon block polyamides, 11carbon block polyamides, thermoplastic elastomers, and mixtures thereof;an inner layer 14 consisting essentially of a thermoplastic materialselected from the group consisting of polychlorotrifluoroethylene,ethylene tetrafluoroethylene copolymers, and mixtures thereof; and anintermediate bonding layer 16 consisting essentially of an extrudablethermoplastic capable of sufficiently permanent laminar adhesion to thepolyamide outer layer 12 selected from the group consisting ofpolyvinylidine fluoride, polyvinyl fluoride, blends of polyvinyl acetateand urethane, and mixtures thereof.

In summary, the third embodiment of the multi-layer tubing 10 comprisesan outer layer 12 consisting essentially of a thermoplastic 6-carbonblock polyamide; an inner layer 14 consisting essentially of athermoplastic material selected from the group consisting ofpolychlorotrifluoroethylene, ethylene tetrafluoroethylene copolymers,and mixtures thereof; and an intermediate bonding layer 16 consistingessentially of an extrudable thermoplastic capable of sufficientlypermanent laminar adhesion to the polyamide outer layer and selectedfrom the group consisting of polyvinylidine fluoride, polyvinylfluoride, blends of polyvinyl acetate and urethane, and mixturesthereof.

In summary, the fourth embodiment of the multi-layer tubing 10 comprisesan outer layer 12 consisting essentially of a thermoplastic materialselected from the group consisting of 12 carbon block polyamides, 11carbon block polyamides, zinc chloride resistant 6 carbon blockpolyamides, thermoplastic elastomers, and mixtures thereof; a polyamideinner layer 14 selected from the group consisting essentially of athermoplastic material selected from the group consisting of 12 carbonblock polyamides, 11 carbon block polyamides, zinc chloride resistant 6carbon block polyamides, thermoplastic elastomers, and mixtures thereof;and an intermediate bonding layer 16 consisting essentially of anextrudable thermoplastic capable of sufficiently permanent laminaradhesion to the outer and inner layers to prevent delamination during adesired lifetime of the multi-layer tubing, the bonding layer 16 being apolyester thermoplastic derived from ethylene glycol selected from thegroup consisting of polybutylene terephthalate, polyethyleneterephthalate, polyteremethylene terephthalate, and mixtures thereof.

In summary, the fifth embodiment of the multi-layer tubing 10 comprisesan outer layer 12 consisting essentially of a thermoplastic materialselected from the group consisting of 12 carbon block polyamides, 11carbon block polyamides, zinc chloride resistant 6 carbon blockpolyamides, thermoplastic elastomers, and mixtures thereof; an innerlayer 14 consisting essentially of a thermoplastic material selectedfrom the group consisting of polyvinylidine fluoride, polyvinylfluoride, a graft copolymer of the preceding materials together with afluorine-containing polymer such as copolymers of vinylidine fluorideand chlorotrifluoroethane, a copolymer of a vinyl fluoride andchlorotrifluoroethylene, the vinyl fluoride material selected from thegroup consisting of polyvinylidine fluoride, polyvinyl fluoride, andmixtures thereof; a copolymer of vinyl fluoride material and ethylenetetrafluoroethylene; and a non-fluorinated elastomer, and mixturesthereof; and an intermediate bonding layer 16 consisting essentially ofan extrudable thermoplastic capable of sufficiently permanent laminaradhesion to the outer layer 12 and inner layer 14, the bonding layer 16being a polyvinyl fluoride compound selected from the group consistingof polyvinylidine fluoride polymers, polyvinyl fluoride polymers, andmixtures thereof; a vinylidine fluoride-chlorotrifluoroethylenecopolymer; and a polyamide material selected from the group consistingof 12 carbon block polyamides, 11 carbon block polyamides, 6 carbonblock polyamides, and mixtures thereof.

In summary, the sixth embodiment of the multi-layer tubing 10 comprisesan outer layer 12 consisting essentially of a thermoplastic 6-carbonblock polyamide; an inner layer 14 consisting essentially of athermoplastic 6-carbon block polyamide; and an intermediate bondinglayer 16 consisting essentially of an extrudable thermoplastic capableof sufficiently permanent laminar adhesion to the outer layer 12 andinner layer 14, the bonding layer 16 selected from the group consistingof co-polymers of substituted or unsubstituted alkenes having less thanfour carbon atoms and vinyl alcohol, alkenes having less than fourcarbon atoms and vinyl acetate, and mixtures thereof.

While preferred embodiments, forms and arrangements of parts of theinvention have been described in detail, it will be apparent to thoseskilled in the art that the disclosed embodiments may be modified.Therefore, the foregoing description is to be considered exemplaryrather than limiting, and the true scope of the invention is thatdefined in the following claims.

1-34. (canceled)
 35. An elongated multilayer tubing comprising: a firstlayer disposed radially innermost and having an inner surface capable ofprolonged exposure to a fluid containing hydrocarbons and an outersurface disposed essentially coaxial to the inner surface, the outersurface spaced a first radial thickness from the inner surface, thefirst layer containing an extrudable, melt-processible thermoplasticselected from the group consisting of fluoroplastics, polyamides,thermoplastic elastomers, and mixtures thereof; a second layer having asecond radial thickness, an inner surface, and an outer surface disposedessentially coaxial to the inner surface, the second layer consistingessentially of an extrudable, melt-processible thermoplastic capable oflaminar adhesion with the first layer; a third layer having a thirdradial thickness greater than the thickness of the first layer, thethird layer connected to the second layer and consisting essentially ofan extrudable, melt-processible thermoplastic.
 36. The elongatedmultilayer tube of claim 35 wherein the second layer comprises at leastone of thermoplastic polyesters, fluoropolymers, copolymers of alkenesand vinyl alcohol, copolymers of alkenes, and vinyl acetate, and blendsof polyvinyl and urethane.
 37. The elongated multilayer tube of claim 35wherein the third layer has a radial thickness between 50 and 70 percentof the total tube wall thickness.
 38. The elongated multilayer to be ofclaim 35 wherein the first, second, and third layers provide a tubingstructure resistant to passive hydrocarbon permeation.
 39. The elongatedmultilayer tube of claim 35 wherein the extrudable melt-processiblethermoplastic employed in the inner layer is: a polyamide selected fromthe group consisting of Nylon 12, Nylon 11, Nylon 6, and mixturesthereof; a fluoropolymers selected from the group consisting ofpolychlorotribluoro ethylene, ethylene tetrafluoroethylene copolymers,graft copolymers of at least one of vinylidine fluoride andchlorofluoroethane with polychlorotrifluoroethylene, graft copolymers ofat least one of vinylidine fluoride and chlorotrifluoroethane withethylene tetrafluoroethane, polyvinylidine fluoride, polyvinyl fluorideand mixtures thereof.
 40. The elongated multilayer tube of claim 35wherein the thermoplastic material of the inner layer is resistant topermeation by aromatic and/or aliphatic compounds contained inautomotive fuel.
 41. An elongated multilayer tubing comprising: a firstlayer disposed radially innermost having a first inwardly oriented faceand a second outwardly oriented face disposed essentially coaxial to theinner surface, the first layer containing an extrudable thermoplasticcomposition; a second layer having an inner surface and an outer surfacedisposed essentially coaxial to the inner surface, the second layerconsisting essentially of an extrudable, melt-processible thermoplasticcapable of laminar adhesion with the first layer; and a third layerconnected to the second layer consisting essentially of amelt-processible thermoplastic containing at least one of polyamides andthermoplastic elastomers.
 42. The elongated multilayer tubing of claim41 wherein the second layer comprises at least one thermoplasticselected from the group consisting of polyvinyl fluoride, polyvinylidinefluoride, polyvinyl acetate-urethane blends, thermoplastic polyesters,polyamides, and mixtures thereof.
 43. The elongated multilayer tubing ofclaim 42 wherein the first layer comprises at least one thermoplasticmaterial compatible with the second layer.
 44. The elongated multilayertubing of claim 42 wherein the third layer has a thickness thatcomprises between 50 percent and 70 percent of a total tubing wallthickness.
 45. The elongated multilayer tube of claim 42 wherein thetubing has an outer diameter below 2.5 inches.
 46. The elongatedmultilayer tube of claim 42 wherein the tubing has a total wallthickness between 0.5 mm and 2.0 mm.